The present invention relates to hydraulic systems and more particularly relates to devices for controlling hydraulic system noise.
Hydraulic oil under pressure is a common means of generating power to move objects or overcome opposing forces. In mobile equipment, a pump is normally the source of pressurized oil. Positive displacement pumps, such as axial or radial piston pumps, or gear pumps combine the flow of individual pumping chambers to produce their total flow. During operation, the pumping chambers each contract and compress discrete volumes of fluid into the system against system pressure. After delivery of the pressurized fluid, the pumping chambers expand and are refilled with low pressure oil from an oil supply port. Variations in flow due to the contraction and expansion of the pumping chambers excites the fluid in the system resulting in pump flow fluctuations or ripples and system pressure fluctuations or ripples. The system pressure fluctuation excites responsive mechanical members causing them to radiate sound.
Heretofore, it has been known to couple various devices, such as accumulators, expansion chambers and Quincke tubes, in hydraulic systems for the purpose of controlling hydraulic system noise. Of these devices, the Quincke tube bears the most physical resemblance to the present invention and therefore will be described in more detail.
In one type of Quincke tube arrangement, the pump output is split to follow first and second branches which are reunited. The branches differ in length by a distance equal to one-half the length of a sound wave induced in the system fluid by the pump. Since the waves traveling through the two branches are out of phase by half a wave length, the waves will cancel where the branches come together and no wave will travel through the system to excite components and cause them to radiate sound. However, the wave length is dependent upon its frequency and the frequency is a function of the pump speed, which in most installations varies with the vehicle engine speed. Therefore, the pump will often be operating at frequencies for which the split Quincke tube arrangement is ineffective.
Now, there is provided a silencer tube arrangement which has the simplicity of the split Quincke tube arrangement but is superior thereto since it is effective over a broad range of sound wave frequencies.